1. Field of the Invention
The present invention relates to data networks and specifically to transferring data over packet switched networks.
2. Background Information
A computer network is a geographically distributed collection of interconnected communication links and segments for transporting data between nodes, such as computer systems. Many types of network segments are available, with types ranging from local area networks (LANs) to wide area networks (WANs). LANs typically connect personal computers and workstations over dedicated, private communications links located in the same general physical location, such as a building or a campus. WANs, on the other hand, typically connect large numbers of geographically dispersed nodes over long-distance communications links, such as common carrier telephone lines. The Internet is an example of a WAN that connects disparate networks throughout the world, providing global communication between nodes on various networks. The nodes typically communicate over the network by exchanging discrete frames or packets of data according to predefined protocols, such as the Asynchronous Transfer Mode (ATM) protocol, Frame Relay (FR) protocol and the Transmission Control Protocol/Internet Protocol (TCP/IP). In this context, a protocol consists of a set of rules defining how the nodes interact with each other.
To interconnect dispersed computer networks, many organizations rely on the infrastructure and facilities of Service Providers (SPs). SPs typically own one or more transport networks that are configured to provide high-speed connections capable of handling traffic for many customers/subscribers. A transport network, as used herein, is a data network used to transport data within a SP's network. In a typical configuration, a customer/subscriber couples its dispersed networks to an edge router configured to enable access to the SP's network. The SP's network may comprise various switches configured to switch traffic between the various edge routers. The routers typically operate at layer-3 (L3) of a communications protocol stack, which is the network layer of the Open Systems Interconnect (OSI) reference model. The switches typically operate at layer-2 (L2) of the communications protocol stack, which is the data-link layer of the OSI reference model.
SPs often provide multiple services to their customers/subscribers, such as FR services and ATM services. Here, an SP may employ parallel or “overlay” networks wherein each network is configured to provide a specific service. For example, a SP that provides a FR service and an ATM service may employ two separate networks where each network provides a separate service. Providing separate networks for separate services, however, is often costly and difficult to manage; thus, many SPs employ a “converged network” to provide various services. A converged network is a network that converges various different services onto a single network, such as an optical network. Converged networks are often called “transport networks” in that they usually act only to transport various services' data from one point in the SP's network to another point in the network.
One way to implement a converged network is to employ a technique called “pseudo wire emulation edge-to-edge” (PWE3). PWE3 is described in S. Bryant et al., “PWE3 Architecture,” draft-ietf-pwe3-arch-06.txt available from the Internet Engineering Task Force (IETF). PWE3 is a technique that emulates the essential attributes of a service, such as ATM or FR, over a packet-switched network (PSN), such as a Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH) network, which acts as a transport network. PWE3 utilizes pseudo wires (PWs), which are mechanisms that emulate the essential attributes of a particular service.
In a typical PWE3 arrangement, a customer's data is encapsulated at the ingress point (e.g., an “ingress” edge router”) in the SP's network. The encapsulated data is transported over the SP's transport network via a predefined path, such as an IP path or a Multiprotocol Label Switching (MPLS) path, to an egress point in the SP's network (e.g., an “egress” edge router). The data is decapsulated at the egress point and delivered to the customer's remote network coupled to the egress point.
One problem associated with PWE3 implementations is that they often require both data-link layer and network layer support. For example, a network that employs the MPLS protocol to transfer data across PWs in a PWE3 network typically requires establishing a L3 infrastructure that may include defining sub-networks and implementing various routing and distribution protocols, such as the Open Shortest Path First (OSPF) routing protocol and the Label Distribution Protocol (LDP). Setting up a L3 infrastructure is often arduous and may require specialty knowledge of the protocols utilized in the infrastructure. SPs typically utilize L2 transport networks that often do not require a L3 infrastructure in order to operate. That is, these networks often transport data through the network using L2 switching techniques. To provide PW support as defined by PWE3, a SP would have to develop a L3 infrastructure within its network. Providing such an infrastructure may be costly.